• NeilBrown's avatar
    sunrpc: fix race in new cache_wait code. · 277f68db
    NeilBrown authored
    If we set up to wait for a cache item to be filled in, and then find
    that it is no longer pending, it could be that some other thread is
    in 'cache_revisit_request' and has moved our request to its 'pending' list.
    So when our setup_deferral calls cache_revisit_request it will find nothing to
    put on the pending list, and do nothing.
    
    We then return from cache_wait_req, thus leaving the 'sleeper'
    on-stack structure open to being corrupted by subsequent stack usage.
    
    However that 'sleeper' could still be on the 'pending' list that the
    other thread is looking at and so any corruption could cause it to behave badly.
    
    To avoid this race we simply take the same path as if the
    'wait_for_completion_interruptible_timeout' was interrupted and if the
    sleeper is no longer on the list (which it won't be) we wait on the
    completion - which will ensure that any other cache_revisit_request
    will have let go of the sleeper.
    Signed-off-by: default avatarNeilBrown <neilb@suse.de>
    Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
    277f68db
cache.c 42.4 KB